Published European Patent Application No. 0 251 825 describes a device for depositing epitaxial layers on substrates by using chemical vapor deposition (CVD). This known device comprises a plurality of susceptors that are arranged vertically with respect to the ground. That is, these susceptors are arranged parallel to the direction of the force of gravity. On each susceptor a plurality of substrates are mounted thereon, and each susceptor is rotatable along its longitudinal axis. The susceptors are arranged along a circular curve around a likewise vertically disposed, centrally configured gas-inlet pipe. The gas-inlet pipe includes ports through which process gases flow in order to deposit the epitaxial layers on the substrates. The flow of such process gases toward the substrates is perpendicular to the vertical longitudinal alignment of the susceptors.
U.S. Pat. No. 3,408,982 describes another device for depositing epitaxial layers on substrates by means of CVD. In particular, the device described therein is intended to manufacture silicon epitaxial layers at an operating temperature range of 1190.degree. C. to 1450.degree. C. This known device comprises a plate-shaped susceptor that is disposed horizontally (that is, perpendicularly to the force of gravity). The susceptor is coupled to a rotating shaft that is arranged vertically (that is, parallel to the force of gravity). In one specific embodiment, the substrates are arranged horizontally on the susceptor. The rotating shaft draws the CVD process gases upward into a gas chamber located above the susceptor plate. As the gases enter the gas chamber, they flow through a center portion of the susceptor into a gas chamber. The gases radially expand in a uniform manner inside the chamber, first traveling up and away from the susceptor plate and then back down to strike the substrates in the direction of the force of gravity. Arranged beneath the substrates is an induction heating coil, which has a flat spiral shape referred to as a pancake coil. In another specific embodiment, the susceptor plate is beveled at an angle toward the top at its edges, and the substrates are inwardly inclined on the oblique portion of the susceptor plate to compensate for the centrifugal force. The associated induction coil is likewise disposed at the same angle as the beveled portion of the susceptor plate.
A drawback of the '982 patent is that the electromagnetic forces generated by the induction coils destabilize the intended, designated positions of the susceptor, and consequently, of the substrates as well. As a result, the destabilization of the susceptor positioning introduces undesired variations into the temperature distribution of the substrates.